The present invention relates to a hot plate for a semiconductor producing/examining device mainly used in the semiconductor industry.
In a semiconductor production/examining device and the like such as a device for etching and a device for CVD, there has conventionally been used a heater, a wafer prober and the like in which a base material made of metal such as stainless steel, aluminum alloy is used.
However, such a conventional heater made of metal as describe above has following defects.
First, the plate thickness of such a heater made of metal must be relatively large (15 mm or so), because a metal plate, if the plate thickness thereof is not large enough, generates warp, strain and the like due to the thermal expansion caused by heating, thereby causing breakage or tilting of a silicon wafer set on the metal plate. When the heater plate is made too thick, however, the heater becomes too heavy and bulky, which is also problematic.
In a heater made of metal, the temperature of a face on which an object to be heated such as a silicon wafer is heated (which face will be referred to as a heating face hereinafter) is controlled by changing the magnitude of voltage/electric current applied to a resistance heating element. When the metal plate as a heater is thick as described above, the temperature of the heater plate fails to promptly follow the change in the voltage and/or electric current. In short, temperature controlling cannot be easily performed in a heater made of metal.
In order to overcome such problems as described above, JP Kokai Hei 11-40330 proposes a ceramic substrate (a hot plate) in which a nitride ceramic or a carbide ceramic having high heat conductivity and strength is used as a substrate and a resistance heating element is provided on a surface of the plate-formed body made of such a ceramic by baking metal particles on the substrate surface by sintering.
In a hot plate comprising nitride ceramic and the like as described above, a through hole is generally arranged in a ceramic substrate thereof and a lifter pin (a pin for supporting a silicon wafer and the like) is inserted through the through hole. The object to be heated such as a silicon wafer is supported by the lifer pin and heated in a state that the object to be heated is distanced by the length of 50 to 2000 xcexcm from the heating face of the substrate.
When the object to be heated is heated in such manner by the above-mentioned hot plate, generation of warp, strain and the like is less likely to happen even at a high temperature because the hot plate has higher strength due to the use of ceramic, as compared with a hot plate made of metal. Further, the above-mentioned hot plate made of nitride ceramic and the like exhibits relatively excellent temperature following property to the change of the magnitude of voltage and/or electric current applied thereto.
However, a conventional ceramic substrate made of such a material exhibits relatively poor sintering property and relatively low density of the sintered product, and tends to contain pores therein (refer to JP Kokai Hei 5-8140).
In general, a surface of a ceramic substrate is ground so that the surface is made flat and smooth. However, in the case of a ceramic substrate having pores therein, a perfectly flat and smooth surface cannot be formed because the pores inside the substrate are constantly exposed at the surface even after the grinding. Thus, significant irregularities exist on the surface of a conventional ceramic substrate.
As a result, when an object to be heated is heated in a state that the object to be heated is distanced by a certain distance from the heating face of a substrate, air between the ceramic substrate and the object to be heated cannot flow as laminar flow in a stable manner at a constant rate but the air is divided into a plurality of portions in accordance with the pattern of the respective portion at which concave portions are formed at the ceramic substrate, whereby stagnation occurs in the each portions at which the concave portion is formed.
Further, since the distance between the object to be heated and heating face varies due to the above-mentioned reason, the quantity of heat reaching the object to be heated also varies depending on the portion, whereby the temperature distribution on the heating face is not directly reflected in the object to be heated. In short, in a conventional ceramic substrate, due to the reason as described above, the even distribution of temperature at the object to be heated is not achieved in a satisfactory manner.
The inventors of the present invention have discovered, as a result of a keen study for solving the above-mentioned problems, that incorporating oxygen in the ceramic which constitutes the substrate improves the sintering property of ceramic, whereby pores at a heating face of a hot plate can be substantially eliminated or at least the diameter of the pore can be significantly reduced. The inventors of the present invention have also discovered that such improvement of the sintering property realizes a dense structure of the ceramic substrate, in which grains are bound to each other by a strong binding force, whereby grains are prevented from falling off at the time of grinding and thus the glossiness of the heating face can be enhanced. The present invention has been completed on the basis of the aforementioned discoveries.
Specifically, the present invention provides a hot plate for a semiconductor producing/examining device, comprising a resistance heating element formed on a surface of a ceramic substrate or inside the ceramic substrate, wherein the glossiness of the heating face of above-mentioned ceramic substrate is 1.5% or more.
In the present invention, the above-mentioned ceramic substrate preferably comprises a non-oxide type ceramic which contains oxygen. This is because, by incorporating oxygen into a non-oxide type ceramic, the sintering property of the ceramic substrate is improved, whereby the glossiness thereof can be enhanced by the grinding process.
Further, the above-mentioned ceramic substrate preferably contains 0.5 to 10 weight % of oxygen. This is because, when the above-mentioned ceramic substrate contains 0.5 to 10 weight % of oxygen, the sintering property of the ceramic substrate is improved, whereby the glossiness of the ceramic substrate can be enhanced by the grinding process.
Yet further, the above-mentioned ceramic substrate is preferably subjected to an annealing treatment. This is because the shape of grains present on the surface of the ceramic substrate can be made round by effecting the annealing treatment to the ceramic substrate, whereby the glossiness of the above-mentioned ceramic substrate can be enhanced.
Yet further, the above-mentioned ceramic substrate is preferably subjected to the cold isostatic pressing process before it is sintered. This is because, pores can be completely eliminated from the formed body which has not been sintered yet by carrying out the cold isostatic pressing, whereby the glossiness of the ceramic substrate can be enhanced.